In the provided sentence, there are a few issues to address. The word "slling" appears to be a typographical error and should be corrected to "selling."

Among the options given:

A. slling
B. and
C. are
D. from

The correct answer to identify the mistake in the sentence is **A. slling**, as it is a misspelling of "selling."

So the correct sentence should read: "They used to **selling** clothes and jewelry, and now they are rich from their business."